The Veil

An agent of the National Intelligence Service (NIS) was missing for a year. He joins a criminal organization to find the traitor responsible for what happened to him.
Han Ji Hyuk is the best NIS operative. He is admired and horrified by colleagues for his impeccable track record and ability to carry out missions. He corners the criminal organization when he goes missing, but returns a year later to shake it up again.
So Soo Young is the head of the 4th group of the Crime Information Center, which copes with its duties and solves cases. She loves people very much and especially cares about her teammates.